If you spent $70 billion on something, you would want to know whether you got your money’s worth.

But when you are a New York City politician spending other New Yorkers’ money, you don’t ask that question. Instead, you do what our mayor and City Council members did Sunday when they announced a $70 billion budget — you pat your fellow pols on the back and speak of protecting firehouses and preventing Housing Authority layoffs.

We are a city of 8.4 million people. If you subtract the state and federal contributions to the budget, we’ll spend about $50 billion from city revenues. That’s a huge increase from the $28.9 billion we were spending when Mayor Bloomberg took office.

Here’s the killer: As the Manhattan Institute points out, “had Bloomberg held Gotham’s budget increase to the growth rates of inflation and population, the city would currently be spending $12 billion less a year” — roughly 25 percent of the budget that comes from city revenues.

We could use that savings, given that most of the spending increase has not gone to improving city services. As the Citizens Budget Commission notes, spending on past promises — i.e., pensions, health-care benefits and debt service — will eat up nearly a quarter of our revenues by 2015. That means less money for current operations.

And when they brag they’ve not raised taxes, keep in mind this is a city that now has a top combined federal, state and local income-tax rate (51.7 percent) second only to California’s. And where public-sector unions believe that with Bloomberg out of the way, they will be in a position to squeeze the next mayor and council for back pay.

We would think this faster-than-inflation rise in New York’s budget would be a hot issue for a serious mayoral candidate. But until we hear them raising the question, we’ll ask you: Do you think you are getting your $70 billion worth?